[APML] Photographing other satellites from orbit

[Robert Reeves <reeves10@swbell.net>]

Kind of a slow list tonight.  I guess we are all watching Iraq on the War
Channel.

Anyway, I posted the following on the SeeSat list, but since it involves
celestial photography from the ISS, Ill cross post it here as well.  Long
post follows, hang on!


A while back I mentioned that Rob Matson had perfected an Iridium flare
prediction program for use by the ISS crew.  I reported the initial success
with the program, but after that ISS Science Officer Don Pettit started
reporting a long string of flare misses.  I was starting to get worried, but
Rob was certain of the program's functionality.  The diagnosis of the
problem centered on the ISS being one step ahead of the lastest orbital
elements.  The station had been undergoing a series of reboosts and it seems
it was always a hair off from the latest elements.  In spite of this, Don
said he was having fun just looking for the flares and to keep the
predictions coming.

Things finally stabilized this morning and just before I left for work, Don
sent me a note saying he had sighted flares for four out three predictions.
Darn good odds, I'd say!  Actually, Don had seen an unpredicted fourth flare
of an in-orbit Iridium spare.

Later this evening about my dinner time, Don sent me the first photo of an
Iridium flare taken from orbit.  The photo is embargoed by NASA, but by way
of verbal description, it was taken with 50 mm f/1.2 Nikor on a Nikon D1.
Assuming about a 30 X 40 degree field of view, shows a star field (after a
little Photoshop work) down to about mag 5.5 or 6.  The flare is trailed
aproximately one degree during the exposure and is not tapered at either
end, showing that the exposure began and ended at mid flare.  There is a
station solar panel from one corner about 1/3 the way into field of view and
on the opposire side of the field is some dim, very out of focus equipment
that is obviously located near the window on the outside of the Russian
airlock module.  The view out the station is certainly cluttered!  Both Rob
Matson and I have been trying to identify the star field, but it elludes us.
I have been an astronomer for 40 years and this image star field mystifies
me.

The following is a clip from the note Don sent me about his flare
observations.........

*******************

Robert and Rob:

Good news.  We nailed nailed four out of three predictions!   I took note of
times which you can see below.  I also saw one unpredicted flash, a bright
one of mag  estimated at  -8 which was barely one minute before the
predicted one of -1 mag.  See notes below.  I estimate that all times are
+/- 2 seconds.  We keep accurate GMT clock to less than a second and I
transfer this to the digital camera and use the start image time stamp for
the flash.  Due to the lag between when I first can see the flash and I open
the shutter (have to move my nose out of the window and place the camera on
its mount),  I estimate the two second uncertainty.  The shutter speed was 5
seconds with automatic dark current subtraction ON so I can not take a
sequential shot until 10 seconds after the first was started.  I captured
these flashes on two frames so the duration is at least 15 seconds each,
probably more like 18 to 20 seconds with human delays.   This is great fun
trying to catch these.   Currently I am using the windows in the Russian
airlock which are on the 45 degree diagonal so they look aft-starboard and
forward-port.  Sometimes I can not use the port and starboard facing windows
in the service module due to too much ambient light and the work schedule
which will not allow the lights to be shut off.   The lab window now points
nadir directly at the two pointer stars in the big dipper and precesses
about 1 degree per day.  Attached is a small image of the -5M flash at
18:04.  Looks like you can see some structure on the satellites however it
may be due to shooting out the airlock window at 45 degrees (double pain
with some contamination on the outside surface).  I would like to try to
photograph a bright flash out the lab window using a 180mm f2.8 telephoto to
see if you could see any structure.  I would have to have good pointing
information for that.   It looks like the nighttime predictions for the
brighter flashes is working well.   Great job on the predictions!

Don

*****************

And again, congratulations to Rob Matson for creating this program and
taking the time to support the ISS with this "unofficial" observational
experiment.

Actually, I see great value in the Iridium search by the ISS, even if it
isn't a real part of the ISS science progam.  These guys in orbit are pretty
good engineers, scientists, pilots, etc., but they usually don't have a lot
of seat time just observing the sky and looking for dim transient
phenomenon.  I think the success rate in the flare observation program has
ramped up partly because Don is now deliberately looking for different
phenomena and in the process is unconsciously training training himself to
see what he may have missed earlier due to inexperience.  He is indeed
learning to be a better observer, and this will pay dividends in other ISS
programs.

Robert Reeves                      reeves10@swbell.net
520 Rittiman Rd.                   www.robertreeves.com
San Antonio, Texas 78209    210-828-9036
USA                                     29.484  98.440  200 meters


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